The present study addresses the questions of why some young people eventually become addicted to heroin whereas their friends may experiment with the drug without becoming addicts or may refuse to try heroin at all. The research is based on interviews with 225 black male addicts, experimenters, and non-heroin users from economically deprived neighborhoods on Chicago's south side. Our underlying framework is a sociological "careers" model. We are viewing heroin addiction as a process which can be broken down into the following steps or stages: No heroin use: first use; irregular, sporadic use; regular, intermittent use or "chipping;" and, finally, daily heroin use and physical dependence. Each of these stages represents a choice point. Some people select one alternative which leads to increased involvement in heroin use; others select other alternatives which lead to decreased involvement, or to abandonment of heroin use. To identify the precursor variables that may help to account for willingness to try heroin, all subjects are given a life history interview which examines demographic characteristics, family background, school performance, involvement in drug use and other illegal activities, and attitudes toward heroin. To identify the career contingencies that affect progression from first heroin use to daily use and onset of physical dependence, interviews with heroin using subjects also assess the circumstances of first use, definition of the heroin high, frequency and duration of "chipping," source of support during the chipping stage, occurrence of adverse outcomes, use of other drugs, and response of family members and friends to heroin use.